php worker horizon support gd ext.

php-worker/Dockerfile

@@ -53,6 +53,13 @@ RUN if [ ${INSTALL_BZ2} = true ]; then \
   docker-php-ext-install bz2; \
 fi
 
+#Install GD package:
+ARG INSTALL_GD=false
+RUN if [ ${INSTALL_GD} = true ]; then \
+   apk add --update --no-cache libpng-dev; \
+   docker-php-ext-install gd \
+;fi
+
 #Install GMP package:
 ARG INSTALL_GMP=false
 RUN if [ ${INSTALL_GMP} = true ]; then \